Portable battery-powered instrument for visualizing the peripheral pulse waveform and pulse rate

ABSTRACT

A compact transistorized pulse detector comprising a strain gauge attached to a finger. The output signal is amplified an filtered to trigger a monostable multivibrator, which signal is then integrated to give a readout of the pulse rate on a meter. The pulse waveform is also visually displayed on a small, battery-powered CRT.

United States Patent Phelps et a1. 7

[54] PORTABLE BATTERY-POWERED INSTRUMENT FOR VISUALIZING THE PERIPHERALPULSE WAVEFORM AND PULSE RATE [72] lnventors: Jerry A. Phelps, 6013lnnes Trace Road, Louisville, Ky. 40222; Donald J. Sass, 756 ForestHills Drive S.W., Rochester, Minn. 55901 22 Filed: Feb. 25, 1970 21App1.N0.: 14,143

[52] US. Cl ..l28/2.05 T, 128/2.05 P [51] Int. C1. A6") 5/02 [58] fieldofSearch ..128/2.05 A, 2.05 C, 2.05 M,

128/2.05 P, 2.05 Q, 2.05 R, 2.05 S, 2.05 T, 2.05 V, 2.06 F, 2.06 R

[56] References Cited UNITED STATES PATENTS 3,228,391 1/1966 Fitter etal 128/205 "r [451 Mar. 7, 1972 Pressman et a1. ..128/2.05 A 3,156,23511/1964 J aeger 2,658,505 1 l/ 1953 Sheer 128/205 P 3,154,067 10/1964Stenstrom et a1. 12812.05 P

3,229,686 1/1966 Edmark, Jr.... ...128/2.05 R

3,412,729 11/1968 Smith, Jr. ..128/2.05 R

OTHER PUBLICATIONS Molyneuir et al.; British Journal of Anesthesia, Vol.27, 1955, pp. 261- 263 Primary Examiner-Wi11iam E. Kamm Attorney-R. S.Sciascia and Arthur L. Branning [57] ABSTRACT q 1 c aim, 2 DrawingFigures l5 l6 is 19 20 2:, 22

so Hz 1 LEVEL MONOSTABLE .IAMPLIFIER HF'LTER FILTER DETECTOR oweasnmronMULTMBRATOR INTEGRATOR ETER AUDIBLE SIGNAL emsnnoa I7 26 vznncm.

DIFFERENTIAL DEFLECTION AMPLIFIER PLATES 0F GRT HORIZONTAL HORIZONTALSWEEP DEFLEOTION eeusnnon PLATES OF CRT a4 55, as memum men RESISTORFocus, mom: #2 VOLTAGE VOLTAGE ems INTENSITY, emu SUPPLY (-200 v.1SUPPLY (-IOOOV.) STRING or CRT as a: 32 :1 1 I2 v. s v. 1.5 v. 252,222.,BATTERY BATTERY BATTERY I BATTERY RECHARGING I CIRCUIT Pmmfnm 1 m2 v v v3,646,931

SHEET 2 UP 2 INVENTORS JERRY A. PHELPS DONALD J. SASS ATTORNEY PORTABLEBATTERY-POWERED INSTRUMENT FOR VISUALIZING TIIE PERIPHERAL PULSEWAVEFORM AND PULSE RATE STATEMENT OF GOVERNMENT INTEREST The inventiondescribed herein may be manufactured and used by or for the Governmentof the United States of America for governmental purposes without thepayment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention relates to the field ofelectromechanical sensors and more particularly to the field of sensorsfor displaying the pulse waveform and detecting the pulse rate of thehuman body.

The general method employed in detecting the'pulse rate of an individualinvolves the use of the hands and other sensory organs of the medicalpersonnel attending the patient and in doing so, generally restrict theaction which may be taken to aid the patient. It should be readilyapparent that standard procedures are to a great extent dependent fortheir accuracy upon the skill and ability of the operator. Movement ofthe l arm or body of the patient can interfere with a reading.Furthermore, the procedure is poorly adapted to monitoring the pulserate of an individual where constantly repeated measurements arerequired as during an operation or when a patient is in criticalcondition.

In order to assist medical personnel, certain laboratory instrumentshave been adapted for gathering pulse rate data. The informationreceived in the form of signals from the sensors is generally amplifiedand displayed or recorded for future use in establishing a medicalhistory of the patient. It is highly desirable that sensors used inconjunction with the patient for detecting the pulse rate be of the typethat can be left unattended after being attached to the body or bodymembers. It has been found, however, that such sensors are generallyquite cumbersome and sometimes bulky in their use and therefore do notlend themselves for portable or emergency use.

The electrocardiogram (ECG) commonly recorded during operations, doesnot give the anesthesiologist any indication of tissue blood flow otherthan the heart itself; in fact, peripheral circulation may be absent inthe presence of a normal ECG.

Prior sensors attached to the patients body to detect the pulse havegenerally been photocell detectors, microphones, or piezoelectriccrystals. However, all three types are relatively bulky,makingthem-practically useless in neonates. Commercial photocelldetectors have also caused skin burns during prolonged use.

Commercial pulse monitors are available today, but they usually are usedwithout a peripheral pulse waveform display such as an oscilloscope.These that do use an oscilloscope, however, usually utilize vacuumtubes, and are very bulky and cumbersome. Furthermore, those utilizingcompact oscilloscopes and/or transistors require a source of AC power orhave an extremely small cathode-ray tube and a short operating timebefore battery replacement is necessary. This precludes use of theseinstruments in remote areas, such as field hospitals, or for continuoususe during anesthesia of long duration.

The use of high AC voltage in the vicinity of the operating room, suchas when electrocautery equipment is employed, usually causes the CRTdisplayed waveform to be deflected off-screen because of the electricalinterference. In presently used monitors, the display is interruptedduring the time the electrocautery machine is utilized, plus anadditional l0-20 seconds for the monitor to recover and becomefunctional after the electrocautery is turned off. As the usual patternis intermittent use of the cautery, present monitors cannot recover andmay be interrupted for several minutes at a time.

SUMMARY OF THE'INVENTION A compact, battery-powered, solid-stateinstrument to display the waveform of the peripheral pulse and a realtime readout of the pulse rate during surgery. Theinstrument uses aminiature semiconductor strain gauge attached to the finger or toe of apatient as the pulse detector. Thepulse signal is amplified and any 60Hz. interference filtered out before being displayed on a cathode-raytube. The pulse signal is also passed through a 1 Hz. filter, and thentriggers a level detector whose waveform is differentiated to trigger amonostable multivibrator, whoseoutput is integrated and then displayedon a meter to give the pulse rate. An audible signal for each-pulse canalso be utilized. The instrument may be self-contained within a portableunit which also includes the batteries and the battery rechargingcircuit.

OBJECTS'OF THE INVENTION It is therefore an object of this invention toprovide a miniature pulse detector.

Another object of this invention is to provide a direct display of thepulse rate.

A still further object of this invention is to provide a pulse monitorwhich is portable, lightweight and compact, and which does not requirethe services of highly skilled personnel during the operation thereof.

A further object of the present invention is to provide a completelydependable and reliable automatic pulse monitor.

A further object of the present invention is to provide a continuousdisplay of the pulse waveform.

A further object of the present invention is to provide a pulse monitorthat can operate from a DC source and be entirely self-contained,-including the DC source recharging circuit.

A further object of the invention is to provide for an audible signalfor each pulse signal.

A further object of the invention is to provide for both a visualdisplay of the pulse waveform and a direct readout of the pulse rate inbeats per minute simultaneously.

Yet another object of the present invention is to provide for atransistorized pulse monitor primarily utilizing integrated circuits.

A still further object of the present invention is to provide for apulse monitor with a pulse detector capable for use on neonates.

DESCRIPTION OF THE DRAWINGS Other objects and advantages of the presentinvention will become apparent from the following detailed descriptionof the preferred embodiment thereof, when considered in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a block diagrammatic representation of a preferred embodimentof a pulse measuring and displaying device in accordance withthe presentinvention during utilization by a patient; and

FIG. 2 is an embodiment in which the monitor is portable, andself-contained.

DESCRIPTION OF THE PREFERRED EMBODIMENT The peripheral pulse waveform isan important measure of tissue blood flow, providing an indication ofthe integrity of cardiac and vascular systems. The pulse waveformdetected in the capillary bed is dependent on both arterial inflow andvenous outflow, but the amplitude of the pulse is primarily related tothe arterial supply and therefore is a measure of tissue blood supply.The inherent elasticity of the vessels also plays a part in determiningthe shape of the pulse waveform, but in any one patient this will beconstant and not a factor in the relative changes in amplitudemonitored. The pulse wave detected at a digit can give asemiquantitative measure of tissue perfusion. A decrease in capillaryblood pressure in the digits, although of smaller amplitude, is directlyrelated to a reduction in digital volume, which is considered related todigital blood flow.

A decrease in the amplitude of the digital pulse waveform may be seenprior to any changes in the patients vital signs, as the extremities,and particularly the digits with their rich arterial blood supply, areusually the first areas to undergo compensatory vasoconstriction.

The invention will now be described in detail with particular referenceto FIG. 1, showing the diagrammatic representation of the preferredembodiment.

The apparatus of the present invention utilizes the technique ofapplying a sensor to the distal phalanx of the patients finger 11. Thedetector is a miniature semiconductor strain gauge 13 which is easilyapplied to the distal phalanx of a finger or toe, employing a Velcrocuff 12. It is sufficiently small mm. X 5 mm.) to be used on newborns aswell as adults. The pulse is detected by the strain gauge 13, whichforms one arm of the Wheatstone bridge 14.

The output of strain gauge 13 is an electrical signal that va ries inamplitude in proportion to the pressure acting through an artery wall.Since the heart beats, the flow of blood through the arteries isnecessarily pulsating. Therefore, the electrical signal picked up has asubstantially pulselike waveform.

Due to unbalance in the bridge 14 caused by the pulse, a

, signal is transferred to amplifier 15 to be amplified. The output ofamplifier 15 passes through amplifier and filter 16 which furtheramplifies the signal and removes 60 Hz. interference present. At thispoint part of the signal is fed to a differential amplifier 17 usingbipolar transistors, to provide enough voltage to drive the verticaldeflection plates 26 of the cathode-ray tube (CRT) 25 in a push-pullmanner. The pulse is thus displayed on a cathode-ray tube such as theSylvania 3BGP7 which has a 1%X3-inch face size and is speciallydeveloped for battery-powered oscilloscopes using only 6 percent of thepower required of conventional cathode-ray tubes for the heater element.

The vertical sensitivity adjustment 27, which is part of amplifier andfilter 16, may be adjusted in fixed increments so that the relativechanges in pulse amplitude can be quickly measured followingadministration of an anesthetic or drug, or after an operative maneuver.

A horizontal sweep generator 28 provides a saw tooth waveform whichdrives the horizontal deflection plates 29 of the CRT 25, resulting in afree running sweep.

If a permanent record is required, an X-Y recorder or other pen-typerecording device may be connected to the output of amplifier and 60 Hz.filter 16 and used instead of, or in conjunction with the cathode-rayoscilloscope 25.

The pulse signal, besides being displayed on CRT 25 is further processedto measure the pulse rate. The signal from amplifier and filter 16 isfed to a low-pass (1 Hz.) filter 18 to remove the dicrotic notch causedby aortic valvular closure, which could cause a falsely high pulsereading. The signal then passes through level detector 19, to removebackground noise and provide a step change in voltage, whose outputsignal is differentiated by differentiator 20 to provide a sharpnegative going spike.

The sharply peaked signal from differentiator 20, corresponding to eachpulse, is fed to monostable multivibrator 21 which switches to itsunstable condition when the amplitude of the input signal exceeds apredetermined trigger level and returns to its stable condition after ashort period of time. The output of monostable multivibrator 21, in theform of a rectangular pulse, is fed to the input of integrator (analogfrequency counter) 22, which provides a current directly proportional tothe'pulse rate and is read out on meter 23, which may be a 3-inch, 0 tol milliarnmeter calibrated in beats per minute. The meter scale iscalibrated from 0 to 200 beats per minute (bpm), the reading beingaccurate to :4 bpm.

If desired, an audible signal which sounds for each pulse from leveldetector 19 may be derived from audible signal generator 24, byoperating switch 40.

The electronic circuitry in the apparatus described above is entirelysolid-state (with the exception of the CRT 25) and battery-operated, andmay be contained in one compact unit 30, as shown in FIG. 2. Alsoincluded in the unit are the batteries that power the circuits. Al2-volt battery 31 and a 6-volt battery 32 can provide the positive andnegative supply, respectively, for the integrated circuit operationalamplifiers. The Wheatstone bridge 14 is powered by the 6-volt battery 32and the monostable multivibrator 21 is powered by the l2-volt battery 31as is the audible signal generator 24.

The medium voltage supply 33, which produces 200 volts for thehorizontal and vertical deflection circuits, is generated by aHartley-type oscillator powered by the l2-volt battery 31, The highvoltage supply 34 of l,000 volts is provided by a blocking oscillatorpowered by the 6-volt battery 32. This provides the accelerating beamvoltage, and by a resistor bias string 35, intermediate voltages for thefocus,anode No. 2, grid, and intensity 36 of the CRT 25. A l.5-voltbattery 37 directly powers the heater element 38 of the CRT 25.

A battery recharging circuit 39, contained in the unit, steps down,rectifies, and limits l20-volt AC to the proper DC voltages and currentsfor the three nickel cadmium batteries. A Chicago-Stancor P-8363 may beused for the transformer in this circuit. A three-pole, three-positionfunction switch 41 is used to select the battery recharge, off, or onfunction.

Utilizing this monitor, the systolic blood pressure may be determinedwhen the pulse cannot be easily palpated and when the Korotkoff soundsare difficult to hear. A blood pressure cuff is applied to the sameextremity as the pulse monitor and the blood pressure recorded when thepulse is first detected by the monitor. This technique is helpful ininfants where the oscillimetric method of determining the systolicpressure is unsatisfactory and the flush method impractical duringanesthesia.

Abnormal heartbeats or pulse waveforms may be detected with thismonitor, i.e., premature ventricular contractions with a compensatorypause, pulsus altemans, etc., may be detected. Tissue perfusion duringclosed chest cardiac massage or cardiac catheterization may also bemonitored.

The complete monitor described above can thus provide anesthesiologistswith a visual display of the peripheral pulse waveform and pulse rateduring surgical operations. It can be easily mounted on an anesthesiamachine or intravenous pole in the operating room, and operates fromself-contained rechargeable batteries. It is compact, lightweight,entirely solid-state, operates for a long period of time, has a shortwarmup period and may be used in remote areas. it is a valuable adjunctto the evaluation of the patient's cardiovascular status duringanesthesia as well as providing a continuous readout of the pulse rateand freeing the hands of the anesthesiologist for other duties.

Obviously many modifications and variations of the present invention arepossible in light of the above teachings. it is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

1. Apparatus for detecting the pulse of an individual comprising:

a strain gauge for producing electrical signals representative of thepulse waveform, said strain gauge adapted to be attached to a digit ofsaid individual;

circuitry coupled to said strain gauge for modifying said signals;

a differentiator coupled to said circuitry for differentiating saidmodified signals to provide spike signals;

a monostable multivibrator coupled to said differentiator for producinga rectangular pulse for each spike signal;

an integrator coupled to said monostable multivibrator for integratingsaid rectangular pulses;

a first display means coupled to said integrator for indicat ing thepulse of said individual;

l0l02b 0028 a level. detector coupled to said low-pass filter forproviding a step change in voltage for each pulse signal, said leveldetector also coupled to said differentiator;

an audible signal generator coupled to said level detector for audiblyindicating each pulse signal detected by said strain gauge;

said first display means comprising a milliamrneter; and a seconddisplay means comprising a cathode-ray tube having a very small facesize.

1. Apparatus for detecting the pulse of an individual comprising: astrain gauge for producing electrical signals representative of thepulse waveform, said strain gauge adapted to be attached to a digit ofsaid individual; circuitry coupled to said strain gauge for modifyingsaid signals; a differentiator coupled to said circuitry fordifferentiating said modified signals to provide spike signals; amonostable multivibrator coupled to said differentiator for producing arectangular pulse for each spike signal; an integrator coupled to saidmonostable multivibrator for integrating said rectangular pulses; afirst display means coupled to said integrator for indicating the pulseof said individual; said circuitry comprising a Wheatstone bridgecircuit, wherein said strain gauge is a miniature semiconductor andforms one arm of said Wheatstone bridge circuit whereby said bridgecircuit transmits a pulse signal upon detection of a pulse by saidstrain gauge; amplifier means coupled to said bridge circuit foramplifying said pulse signal; filter means coupled to said amplifier forremoving 60 Hz. interference; a 1 Hz. low-pass filter coupled to saidfilter means for removing the dicrotic notch from the pulse waveform; alevel detector coupled to said low-pass filter for providing a stepchange in voltage for each pulse signal, said level detector alsocoupled to said differentiator; an audible signal generator coupled tosaid level detector for audibly indicating each pulse signal detected bysaid strain gauge; said first display means comprising a milliammeter;and a second display means comprising a cathode-ray tube having a verysmall face size.